The projects outlined in this application extensively utilize genetically altered mice to explore the molecular genetic basis of pediatric cardiac diseases in vivo. These genetic manipulations involve the techniques of pro-nuclear injection to create transgenic animals, ES cell injection into blastocyst to create chimeric animals, and tetraploid fusion to create chimeric animals. Since successful execution of these techniques require both expensive equipment and extensive train of technical personnel, we will utilize a central laboratory to concentrate expertise and share costs. This laboratory will provide expertise, advice, and assistance in the generation and maintenance of genetically altered mice, including prompt and reliable performance of the following techniques: production of transgenic mice by pro-nuclear injection of DNA constructs, production of chimeric mice by blastocyst injection of embryonic stem cells, production of chimeric mice by tetraploid fusion, preservation of mutant mouse stock by embryo cryopreservation, and access to mouse breeding stocks.